Conventionally, a heating and/or air conditioning apparatus for an automotive vehicle includes an air supply duct for delivering external air, i.e. ambient air from outside the vehicle, with this duct dividing into a first branch and a second branch, the first branch having first outlet means into the interior of the vehicle, the second branch comprising a heat exchanger for heating air passing through it, the second branch having second outlet means for delivery of air into the interior of the vehicle, the apparatus further comprising junction means for bringing the first and second branches into communication with each other and control means for adjusting the temperature of the air delivered from the various said outlet means.
The means for regulating the temperature of the air delivered via the outlets may for example be a valve, and is so arranged that this air may be delivered at the same temperature through the first and second outlets, or with the air from the first outlets being at a different temperature from that at the second outlets. In this latter case, the apparatus can function in a "bi-level" manner, in which the temperature levels are stratified in such a way as to cause the temperature to be different as between the first and second branches.
It has however been established that such an arrangement has some disadvantages. In the embodiments known at the present time, the different air outlets include flap valves in the vicinity of their outlets, allowing the flow of air delivered to be regulated. When for example the flap valves of the outlets of the first branch are closed, there is a back flow of air into the junction region, and this back flow mixes with treated air inside the apparatus, so disturbing the temperature of the latter.